Research:Trading and Services

Trading and services

Common mechanics

Barter function

All bartering and services use a common function to evaluate costs. Uses common formula fatigueTerm for each side of a transaction.

defining a function barterOffer :: (Actor npc, int basePrice, bool buyingSelling) -> int offerPrice

if npc is a creature: return basePrice

clampedDisposition = clamp int(npcDisposition) to [0..100]
a = min(pcMercantile, 100)
b = min(0.1 * pcLuck, 10)
c = min(0.2 * pcPersonality, 10)
d = min(npcMercantile, 100)
e = min(0.1 * npcLuck, 10)
f = min(0.2 * npcPersonality, 10)

pcTerm = (clampedDisposition - 50 + a + b + c) * pcFatigueTerm
npcTerm = (d + e + f) * npcFatigueTerm
buyTerm = 0.01 * (100 - 0.5 * (pcTerm - npcTerm))
sellTerm = 0.01 * (50 - 0.5 * (npcTerm - pcTerm))

if buying: x = buyTerm
if selling: x = min(buyTerm, sellTerm)

if x < 1: offerPrice = int(x * basePrice)
if x >= 1: offerPrice = basePrice + int((x - 1) * basePrice)
offerPrice = max(1, offerPrice)

Bartering

Actions affected	On choosing/offering an item to buy/sell
Description	When selecting items to trade.
Implementation status	not started yet
Analysis status	Verified

basePrice = price of prototype item of the same kind, enchanted items have prices set at enchant time and saved with the object
stackSize = number of items in selected stack

if item is a weapon or armor: x = basePrice * (remainingDurability / maxDurability)
if item is lockpick, probe or repair hammer: x = basePrice * (remainingUses / maxUses)
if item is a filled soul gem: basePrice = soul points contained * empty soul gem price
otherwise: x = basePrice

if buying: merchant offer is adjusted by -barterOffer(merchant, x * stackSize, buying)
if selling: merchant offer is adjusted by +barterOffer(merchant, x * stackSize, selling)

Actions affected	On bartering
Description	Includes haggling mechanic.
Implementation status	not started yet
Analysis status	Verified

all prices are negative when player is buying, positive when player is selling

accept if playerOffer <= merchantOffer (same for buy and sell)
if npc is a creature: reject (no haggle)

a = abs(merchantOffer)
b = abs(playerOffer)
if buying: d = int(100 * (a - b) / a)
if selling: d = int(100 * (b - a) / a)

clampedDisposition = clamp int(npcDisposition) to [0..100]
pcTerm = (clampedDisposition - 50 + pcMercantile + 0.1 * pcLuck + 0.2 * pcPersonality) * pcFatigueTerm
npcTerm = (npcMercantile + 0.1 * npcLuck + 0.2 * npcPersonality) * npcFatigueTerm
x = fBargainOfferMulti * d + fBargainOfferBase
if buying: x += abs(int(pcTerm - npcTerm))
if selling: x += abs(int(npcTerm - pcTerm))

roll 100, if roll <= x then trade is accepted
adjust npc temporary disposition by iBarterSuccessDisposition or iBarterFailDisposition

Merchant repair

Actions affected	On opening the repair service window
Description
Implementation status	not started yet
Analysis status	Verified

p = max(1, basePrice)
r = max(1, int(maxDurability / p))

x = int((maxDurability - durability) / r)
x = int(fRepairMult * x)
cost = barterOffer(npc, x, buying)

Trainers

Actions affected	On purchasing training
Description
Implementation status	in progress
Analysis status	Verified, but buggy. See notes for solution.

cost of training a skill = barterOffer(npc, pcSkill * iTrainingMod, buying)

Standard Morrowind uses the current skill value, including fortifies and drains, which allows cheap training exploits with drain spells. A new implementation should use the skill's base value.

Spell merchant

Actions affected	On purchasing a spell
Description
Implementation status	not started yet
Analysis status	Verified

cost of purchasing existing spell = barterOffer(npc, spell.magickaCost * fSpellValueMult, buying)

Actions affected	On purchasing from a spellmaking service
Description
Implementation status	not started yet
Analysis status	Needs testing

y = 0
for each effect in spell:
    x = 0.5 * (effect.magnitudeMin + effect.magnitudeMax)
    x *= 0.1 * effect.magicEffect.baseMagickaCost
    x *= 1 + effect.duration
    x += 0.05 * max(1, spell.radius) * effect.magicEffect.baseMagickaCost

    y += x * fEffectCostMult
    y = max(1, y)
    if effect.flags & CAST_TARGET: y *= 1.5

magickaCost = int(y)
cost of spellmaking = barterOffer(npc, magickaCost * fSpellMakingValueMult, buying)

Enchanting merchant

Actions affected	On purchasing an enchantment
Description
Implementation status	not started yet
Analysis status	Unverified; enchantment points are unspecified

cost of enchanting service = barterOffer(npc, enchantment points * fEnchantmentValueMult, buying)

Travel costs

Physical travel

Actions affected	On travelling via silt strider, boat or similar travel service AI
Description
Implementation status	not started yet
Analysis status	Requires independent testing

dist = distance from player to destination
cost = barterOffer(npc, int(dist / fTravelMult), buying)
time = int(dist / fTravelTimeMult)

Guild guide

Actions affected	On travelling via Mages' Guild teleport service
Description
Implementation status	not started yet
Analysis status	Verified

cost = barterOffer(npc, fMagesGuildTravel, buying)